The intertidal sea star Pisaster ochraceus lives in a wide range of wave-exposure conditions in the northeastern Pacific. Its body form and tube foot tenacity are both highly correlated with wave exposure. On wave-exposed shores sea stars attach to the substrate with higher tenacity, weigh significantly less per unit arm length, and have a narrower body and arms. Water velocity explained over 99% of the variation in average body shape and 92% of the variation in average tenacity. Reciprocal transplants revealed that both traits responded plastically to changes in wave exposure, so the variation is therefore primarily ecophenotypic. This plasticity is likely also adaptive, allowing Pisaster to respond to variation in flow in both space and time. Both phenotypic responses probably act to reduce dislodgement risk – changes in tenacity influence attachment force and changes in body form modify the drag and lift experienced, which are the main effectors of dislodgement.

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